There are many instances where detecting and locating a source of energy is important. For example, in commercial aircraft there is a concern among pilots and air carriers that personal electronic devices (PEDs) may interfere with aircraft operation and safety. In certain business environments is it important to determine if unauthorized wireless devices are in use in controlled areas. Providing location information on locating transmitters is important in the mining industry.
Standard techniques that can be used to locate emitters in free space often do not work well in confined spaces such as buildings, tunnels, or within aircraft. These techniques often reply on direction antennas (angle of arrival), or signal timing between or among a small number of sense antennas (time difference of arrival).